1. Field of the Invention
The present invention relates to a display device for a telescope system, and particularly relates to a display device for a telescope system that has both range finding and electronic displaying functions
2. Description of Prior Art
The optical system of a conventional telescope or sight is generally composed of an objective, an image erecting lens group, an eyepiece and a scale board with a reticle. The scale board is marked with a rough rangefinding scale. By referring to the rangefinding scale, the observer can rapidly and roughly estimate the range to a target. Therefore, such a conventional telescope or sight may be used as a simple rangefinder.
However, the range estimation by conventional telescope or sight is mostly dependent on the experience of the observer that may bring large tolerance. Accordingly, a laser telescopic sight progressively takes the place in the precise shooting and rangefinding fields. A conventional laser telescopic sight has been disclosed in U.S. Pat. No. 5,771,623 issued on Jun. 30, 1998. The conventional laser telescopic sight generally comprises an objective, a laser transmitter (such as a laser diode, LD), a laser receiver (such as an avalanche photoelectric diode, APD), a range indicator (such as a light emitting diode, LED), three sets of prisms coated with dichroic films, an image erecting lens group and an eyepiece. The laser transmitter and the laser receiver both constitute a laser rangefinder of the telescopic sight. The laser rangefinder operates on a principle of measuring a travel period from emission of a laser pulse or laser pulse sequence by the laser transmitter, via pulse reflection by a target aimed at, to reception of a reflected pulse by the laser receiver. One half of this travel period, multiplied by the constant speed of light, yields the distance between the telescopic sight and the target. The distance calculation is performed by a calculation device or program disposed within the telescopic sight.
In the conventional sight as described above, in order to see both the target image and the electronic signal that carries the distance and direction information of the target, an optical display system must be incorporated into the sight. A common telescope system generally only requires the target image to be focused onto an image plane positioned in front of the eyepiece, so that the observer can simultaneously see the target image and the electronic signal through the eyepiece. This is conventionally achieved by employment of a right angle prism, a roof prism or a Porro prism. However, for a sight system with magnification function, a magnification system must be positioned in front of the eyepiece, and the electronic signal is conventionally focused onto an image plane in front of the magnification system. This will result in variation of the image size of the electronic signal along with the magnification variation. Consequently, the magnification ratio cannot be too high, normally below 3 times, otherwise the image size of the electronic signal will be too small in case of a lower magnification, or too large in case of a higher magnification. In addition, the image position of the electronic signal also shifts with magnification variation, and the image brightness of the displayed electronic signal is also changed. This adversely affects vision feeling and electronic control.
Therefore, a display device for a telescope system is desired, which can maintain constant image size and brightness of the displayed electronic signal and which can image the electronic signal onto any position within the telescope field of view.